1. Field of the Invention
The present invention relates to a solid-state imaging device and a manufacturing method therefor, and more particularly to a structure of transfer electrodes and a method of forming the structure.
2. Description of the Related Art
A CCD (Charge Coupled Device) type solid-state imaging device used in an area sensor, digital still camera, etc. includes a plurality of transfer electrodes for transferring signal charges from a photoelectric converting portion. The transfer electrodes are arranged adjacent to each other on a charge transfer line formed in a device substrate and sequentially driven.
In such a CCD type solid-state imaging device, a reduction in resistance of each transfer electrode is required for a large angle of view and a high transfer ratio. In the case that each transfer electrode is formed of a metal material having light shieldability, the resistance of each transfer electrode can be reduced and a photodiode forming area can be increased because each transfer electrode need not be covered with a light shielding film. Accordingly, a larger quantity of light can be detected by the photodiodes and an improvement in sensitivity characteristics can therefore be expected.
Techniques of forming transfer electrodes by using a metal material are described in Japanese Patent Laid-open Nos. 2003-78126 and 2007-12677, for example. According to the technique described in Japanese Patent Laid-open No. 2007-12677, polycrystalline silicon electrodes are first formed as dummy electrodes, and the dummy electrodes are next removed to form recesses. Thereafter, a metal film is formed so as to fill these recesses with a metal material, and an excess part of the metal material is next removed by CMP (Chemical Mechanical Polishing) to thereby form the transfer electrodes from the metal material.